Indoor air quality is an important issue which is closely related to human health and comfort. Pollution of indoor air constitutes a significant risk factor for various health problems in view of the fact that many people spend most of their time, for example, more than 90% of their time, indoors. In general, air pollutants can be one or more of particle pollutants, gas pollutants and microorganisms. Particle pollutants can be removed from air by applying an appropriate air purification system such as a system which is equipped with high efficiency HEPA filters. Microorganisms which are usually present on the particles can also be removed from air in that way.
The invention relates to the field of removing gas pollutants from air or another gas that needs to be purified. Gas pollutants include both organic gases and inorganic gases. Well-known examples of organic gas pollutants are formaldehyde and volatile organic compounds (VOCs) like benzene, toluene and xylene. Inorganic gas pollutants are gases like CO, CO2, NO2, SO2 and NH3. It is common use to apply an activated carbon filter for removing gas pollutants from air. Also, it is known to apply a photocatalytic oxidation method.
US 2008/135060 A1 discloses a filter element comprising a substrate coated with an acetoacetate-functional polymeric material that reacts with and removes aldehydes present in a gas such as air. The function of the filter elements is based on the fact that gaseous aldehydes such as formaldehyde, acetaldehyde and acrolein may be removed permanently from air or other gaseous environments or media such as tobacco smoke by contacting a gas containing one or more aldehydes with a filter element comprising a substrate, e.g. a filter support material, and a polymeric composition containing an acetoacetate residue, wherein the polymeric composition is selected from condensation polymers, addition polymers, epoxy resins, polysiloxanes, cellulose and cellulose esters.
Effective and simple removal of gas pollutants is realized when liquid solution adsorbents, i.e. liquid solutions containing suitable chemicals, are applied. However, the application of using a liquid in the process is limited due to a relatively small size of the gas-liquid contact area. Also, it may be disadvantageous to have increased humidity on the basis of the presence of the liquid, and the liquid may be difficult to recycle. It is known to increase effectiveness of the application of liquid solution adsorbents by providing a hydrophilic substrate such as a piece of paper for incorporating the adsorbents. However, one of the disadvantages of this method is that only the chemicals at the exterior surface of the substrate are involved in the reaction which is necessary for removal of gas pollutants, wherein most of the chemicals are present inside the substrate and cannot effectively join the reaction as a consequence thereof. Hence, when the surface chemicals have been reacted, the maximum lifetime of the filter element is reached. All in all, the filter element comprising the hydrophilic substrate involves many disadvantages, including low liquid reaction efficiency, short life time and waste of chemicals.